The present application relates to a nonaqueous electrolyte and a nonaqueous electrolyte battery. In particular, the present application relates to a nonaqueous electrolyte and a nonaqueous electrolyte battery capable of keeping excellent battery characteristics under a low temperature environment and a high temperature environment.
In recent years, a number of portable electronic appliances such as a camera-integrated VTR, a digital still camera, a mobile phone, a personal digital assistant and a laptop computer have appeared, and it is contrived to achieve downsizing and weight reduction thereof. With respect to batteries, in particular, secondary batteries as a portable power source for such an electronic appliance, research and development have been actively conducted for the purpose of enhancing the energy density. Above all, lithium ion secondary batteries using carbon for a negative electrode active material, a lithium transition metal complex oxide for a positive electrode active material and a carbonate mixture for an electrolytic solution are proposed. Such batteries are widely put into practical use because a large energy density is obtained as compared with lead batteries and nickel cadmium batteries which are a nonaqueous electrolytic solution secondary battery of the related art. In particular, recently, it is contrived to modify the positive electrode active material or to enhance the charge voltage for the purpose of realizing a higher capacity.
In such batteries with a high capacity, the portability is enhanced by downsizing of electronic appliances, and an opportunity of use upon being brought out outdoors increases. That is, it may be considered that the electronic appliances are used under a low temperature environment and a high temperature environment. When placed in a charged state under a high temperature environment, a positive electrode is deteriorated due to a reaction between an electrolytic solution and a positive electrode active material on the surface of the positive electrode, resulting in a lowering of the capacity after long-term storage. Also, when placed under a low temperature environment, the ion conductivity is lowered, resulting in a lowering of the capacity.
Then, in order to solve these problems, Patent Document 1 (JP-T-8-511274) describes the use of lithium bis(fluorosulfonyl)imide (LiFSI) as an electrolyte salt. Patent Document 2 (JP-A-2004-165151) reports that when an electrolytic solution containing a lactone as a solvent and lithium bis(fluorosulfonyl)imide (LiFSI) as an electrolyte salt is used, the stability is excellent at high temperatures or during storage. Patent Document 2 also reports that the stability is more enhanced by using, as an additive, vinylene carbonate, vinyl ethylene carbonate, phenyl ethylene carbonate or propanesultone. Patent Document 3 (JP-A-2009-70636) discloses a battery containing a quaternary ammonium cation and containing a (fluorosulfonyl)imide (FSI) anion and an inorganic anion.